A control apparatus of an AC motor improves an electric current estimation accuracy of the AC motor. The control apparatus includes an electric current estimation unit that repeatedly performs an inverted dq conversion, a dq conversion, and a correction process. Based on a d/q axis electric current estimate values of a previous cycle, the inverted dq conversion calculates an electric current estimate value of a sensor phase. The dq conversion calculates a d/q axis electric current correction values based on an electric current estimation error of the sensor phase, which is derived from the electric current estimate value and the electric current detection value detected by an electric current detector. The correction process calculates the d/q axis electric current estimate values of a current cycle by correcting the d/q axis electric current estimate values of the previous cycle by using the d/q axis electric current correction values.